JPH11259986A - Waveform equalizer and data reproducing device using the equalizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a reading signal by surely correcting asymmetry of the reading signal. SOLUTION: This equalizer is for executing waveform equalizing for a reading signal, and is provided with an inclination determining means 400 for detecting the upward and downward slope parts of the reading signal, a filter 100 for filtering the reading signal, and a characteristic switching means 300 for switching the frequency characteristic of the filter according to the determining output of the inclination determining means 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizer, and more particularly, to a waveform equalizer that performs waveform equalization on a read signal of a recording medium. The present invention also relates to a data reproducing device using such a waveform equalizer.

[0002]

2. Description of the Related Art In an optical disk recording information reproducing apparatus which is one of the recording medium reading systems, a photoelectric conversion output of reflected light from the optical disk obtained by irradiating the optical disk with reading light is converted into an RF signal or a reading signal. A technique is known in which the waveform of the read signal is corrected by using a waveform equalizer to reduce the waveform interference, and then subjected to a binarization process to generate a digital read signal.

In such a technique, the asymmetry of the read signal can be corrected in the binarization process. More specifically, there is variation in the power of the recording light used for mastering at the time of recording information on the optical disk and the length of pits as recording marks actually formed on the optical disk due to this. Generally, if the recording light power is not appropriate, a phenomenon occurs in which each formed pit becomes slightly longer or shorter by the same amount before and after the pit in the longitudinal direction. That is, the symmetry between the pit and the non-pit cannot be maintained. This phenomenon is called asymmetry.

FIG. 1 shows a state in which a read signal obtained by reading a recording signal without asymmetry is binarized with a predetermined threshold value (zero in this example). in this case,
An appropriate binary read signal having a duty ratio of 50% corresponding to the recording signal can be obtained in both the high-level portion and the low-level portion. On the other hand, when a recording signal having asymmetry is read, as shown in FIG. 2, a read signal having an appropriate threshold value changed can be obtained. In addition, the low-level portion becomes inappropriate because it does not correspond to the recording signal.

[0005] Asymmetry is not completely suppressed in the mass production process of optical discs. Further, the asymmetry of the read signal itself in the disk reading system varies depending on the wavelength of the read laser light of the applied optical pickup. CD (Compact Disk) type discs are standardized so that the asymmetry falls within a certain range, and in the reading system, the characteristics of the read signal assumed according to the CD method are used to asymmetry. Is automatically corrected. More specifically, C
EFM (Eight to Fourteen Modulatio) recorded on D
n) The point where the DC component of the signal itself is zero, and the length of the logical value 0 or 1 of the data by EFM (so-called run length) is 3T to 11T (1T is the period of one channel bit).
Utilizing a characteristic such as a point that is limited to the following, the center of the eye pattern of the read signal is tracked and detected, and the read signal is binarized using the detected center level as a threshold value.

The ability to follow the eye pattern in such a technique has been considered to be sufficient for a CD-type disc. However, DVDs that are currently in practical use
(DIGITAL VIDEO DISC or DIGITALVERSATILE DISC)
In a disk having a larger capacity and higher density recording than that of a CD, the pit length corresponding to each run length of recorded data is considerably shorter than that of a CD, and the ability to follow the eye pattern by the above method is not sufficient. May be sufficient.

In the case of recording using 8/16 modulation of DVD as an example, in the case of recording with a short pit length, if the recording power deviates from the optimum value, the eye pattern of the 3T signal which is the minimum run length in the read signal is obtained. The center shifts from the center of the eye pattern of the signal of 4T or more, and the read signal deteriorates. The center of the eye pattern corresponds to a threshold value such that the pulse width of a signal obtained by binarizing the read signal is equal to the pulse width of the recording signal.

Here, the change of the center of the eye pattern with respect to the recording power is schematically shown in FIG.
Since the resolution limit of an LBR (laser beam recorder), which is a signal recording system for an optical disk, is close to the limit, the center position of the 3T signal eye pattern changes sensitively to the recording power. That is, as shown in the drawing, the characteristic of the 3T signal has a large slope.

On the other hand, since the signal of 4T or more has a margin in the resolution of the LBR, the change of the signal of 4T or more with respect to the recording power at the center of the eye pattern is gradual. Therefore, when the recording power is smaller than the optimum value, 3T
Is brighter (closer to the mirror level) than the center of the eye pattern of the signal of 4T or more. That is, as shown in FIG. 4, when the recording power is too small, the signal of 3T is converted to 4T when binarizing the read signal.
The appropriate threshold is higher than the above signals. On the other hand, when the recording power is larger than the optimum value, the light becomes darker than the center of the eye pattern of the signal of 4T or more. That is, FIG.
As shown in (2), at the time of excessive recording power, when binarizing the read signal, the appropriate threshold value of the 3T signal is lower than that of the signal of 4T or more.

Therefore, when the 3T signal and the 4T or more signal are binarized at the same threshold value, the shift of the center of the eye pattern of the 3T signal becomes a shift of duty due to asymmetry, and jitter occurs in the read signal. Let it do. As described above, due to the lack of resolution of the LBR, the eye center of the eye pattern of the 3T signal mainly responsible for the shortest pit changes sensitively to the recording power, thereby narrowing the recording power margin. The fact that the signal carrying the shortest pit has a considerable effect on the quality of the read signal is a problem that has not been seen in CDs and the like.

In the case of a write-once or rewritable recording medium, since the recording medium to be used, the recording device, and even the recording environment are left to each user, asymmetry due to variations in recording power is reduced. It is expected to occur, and it is extremely important to deal with such asymmetry in order to maintain high playability in a product.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to improve the quality of a read signal by reliably correcting asymmetry in the read signal. And to provide a data reproducing apparatus using the same.

[0013]

SUMMARY OF THE INVENTION A waveform equalizer according to the present invention is a waveform equalizer for performing waveform equalization on a read signal, and a slope discriminator for discriminating a rising slope portion and a falling slope portion of the read signal. Means, a filter for performing a filtering process on the read signal, and characteristic switching means for switching a frequency characteristic of the filter in accordance with a discrimination output of the inclination discriminating means.

In the waveform equalizer according to the above aspect, the filter includes a first filter for setting a frequency characteristic for the rising slope and a second filter for setting a frequency characteristic for the falling slope. And the characteristic switching means can select one of the output signals of the first and second filters and use it as an output signal of the waveform equalizer. Also,
The filter may be an FIR filter, and the characteristic switching unit may switch the frequency characteristic by changing a value of a tap coefficient of the FIR filter.

Further, the frequency characteristic under the discrimination of the rising slope is set according to a sample value near zero crossing in the corresponding rising slope of the read signal, and the frequency characteristic under the discrimination of the falling slope is set. May be set according to a sample value near the zero crossing in the corresponding falling slope of the read signal.

A data reproducing apparatus according to the present invention is a data reproducing apparatus which obtains reproduced data by binarizing a read signal of a recording medium, and a sampling means for sampling the read signal to generate a sample value series read signal. A slope determining means for determining a rising slope part and a falling slope part of the sample value series read signal, a filter for performing a filtering process on the sample value series read signal, and a filter A waveform equalizer including a characteristic switching unit for switching frequency characteristics, and a binarizing unit for binarizing an output signal of the waveform equalizer to generate the reproduction data.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 5 shows a schematic configuration of a disk recording information reproducing apparatus to which the waveform equalizer according to the present invention is applied. In FIG. 5, an optical disk 1 as a recording medium
The reading light is emitted from the optical pickup 3 while being rotated by the spindle motor 2. The reading light is subjected to optical modulation corresponding to, for example, pits as recording information or recording marks on the recording surface of the disk 1 and returns to the pickup 3 as reflected light including such recording information components. The pickup 3 receives the reflected light and generates an electric signal corresponding to the light receiving level or the light receiving state as an RF signal or a read signal.

A read signal from the pickup 3 is supplied to an A / D converter 5 via an RF amplifier 4. The A / D converter 5 digitizes an input analog read signal at a predetermined sampling rate and a predetermined number of quantization bits. By this digitization, a read signal of a sample value series (hereinafter, may be abbreviated as “read signal” as appropriate) is generated.

The read signal from the A / D converter 5 is supplied to a waveform equalizer 6. The waveform equalizer 6 is one of the main features of the present invention, and has a function of correcting asymmetry. The details will be described later. The output signal of the waveform equalizer 6 is supplied to a binarization circuit 7, where the read signal binarized as a data series of logical values 1 and 0 is converted into a reproduced data signal (not shown) as a reproduced data signal. It is supplied to the processing system.

Next, the waveform equalizer 6 will be described in detail. First, the basic configuration and operation principle of such a waveform equalizer will be described. In FIG. 6, this waveform equalizer is A /
A POS filter 10 serving as a first filter and a NEG filter 20 serving as a second filter to which a read signal converted into a sample value series is supplied from the D converter 5, and a selection circuit 30 for selecting an output of these filters. Be composed.

The POS filter 10 includes an FIR filter, and adaptively controls a tap coefficient of the read signal based on a deviation from zero of a sample value signal near a zero cross in the read signal. The NEG filter 20 also has
It includes an IR filter, and adaptively controls a tap coefficient of the filter based on a shift from zero of a sample value signal near zero cross in the read signal.

However, the POS filter 10 uses a sample value signal near zero crossing in a level rising slope (hereinafter abbreviated as a rising edge) of the read signal waveform, and the NEG filter 20 performs a level falling slope of the read signal waveform. A tap coefficient is controlled using a sample value signal near a zero cross in a section (hereinafter, abbreviated as a falling edge).

The selection circuit 30 outputs the output signal of the POS filter 10 when the read signal has a rising edge, and outputs N when the read signal has a falling edge.
The output signal of the EG filter 20 is controlled so as to be relayed to a binarization circuit (or a 0/1 determination circuit) 7 at a subsequent stage. That is, the selection circuit 30 outputs the rising edge of the read signal /
Selection switching is performed according to the falling edge identification information.

According to such a configuration, asymmetry can be corrected based on the following principle. For example,
As shown in FIG. 7, consider a case where the center of the eye pattern of the 3T signal in the read signal is shifted below the standard position (read signal indicated by a white circle). In this case, the read signal is set to 2 with the zero level corresponding to the standard position as a threshold.
When the binarization is performed, the rising edge of the binarized read signal (the zero-cross point of the level rising portion) lags behind the rising edge of the recording signal. Also, the falling edge of the binarized read signal (the zero-cross point at the level lowering portion)
This means that the signal has advanced beyond the falling edge of the recording signal.

Therefore, the frequency characteristics (delay and / or amplitude characteristics) of the filter are switched between the rising edge portion and the falling edge portion, and the signal portion of the rising edge is read as indicated by a read signal indicated by a black circle. By advancing the phase and delaying the phase of the signal portion at the falling edge, the deviation of the asymmetry (duty) is corrected.

When the center of the eye pattern is shifted upward, the asymmetry can be corrected by reversing the phase shift direction with respect to each edge. Thus, the rising edge of the read signal (PO
Since it can be understood that the direction to shift the phase between the S edge) and the falling edge (NEG edge) has different jitter components, the POS filter 10 and the POS filter 10 have to remove the jitter components corresponding to each edge. The characteristics of the NEG filter 20 are set, and these are switched in accordance with the edges to perform waveform equalization for proper asymmetry correction.

The width of change of the appropriate threshold value by asymmetry as shown in FIG. 7 substantially corresponds to the amount by which the sample values P0p and P0n near the zero cross at both the rising and falling edges are to be phase-shifted.
Therefore, detecting such sample values P0p and P0n,
By setting the characteristics of each filter according to the detected value, appropriate asymmetry correction is achieved.

Next, a specific configuration of the waveform equalizer will be described. FIG. 8 shows the configuration of a waveform equalizer according to the first embodiment. A read signal converted into a sample value series by the A / D converter 5 is supplied to the FIR filter 100. The FIR filter 100 is configured as shown in FIG.

That is, the sampled signal sequence, that is, the read signal converted into a digital signal having a predetermined number of quantization bits for each sampling period, is supplied to a system composed of cascade-connected five-stage unit delay element groups D1 to D4. The unit delay element groups D1 to D4 provide a time delay equal to the sampling period of the input signal, and the output of one unit delay element group is the input one sampling time before. Each tap output, that is, an input signal and an output signal of each unit delay element group are individually supplied to multipliers M0, M1, M3, and M4 as one input.

The other inputs of the multipliers M0, M1, M3, M4 are provided with tap coefficients ki: ｛k2, k1, k-1, k-, respectively.
A value of 2｝ is supplied. The results of the multiplication by the multipliers M0, M1, M3, and M4 are added by the adder A, and the addition result is derived as an output signal of the FIR filter 100, that is, a read signal after waveform equalization. The tap coefficient ki is, as shown in FIG. 8, the POS tap coefficient kp controlled by the first filter control system 1A by the POS zero-cross detector 1A1 and the POS edge coefficient control circuit 1A2, and the NEG zero-cross detector 1B1. Filter control system 1 by NEG and NEG edge coefficient control circuit 1B2
One of the NEG tap coefficients kn controlled by B is selected by the selection circuit 300.

The POS tap coefficient kp is calculated by the POS edge coefficient control circuit 1A2 based on the correlation between the sample value closest to the zero cross at the POS edge detected by the POS zero cross detector 1A1 and each corresponding tap output. The sample value closest to the zero cross is set to a value that converges to zero. The NEG tap coefficient kn is determined by the NEG edge coefficient control circuit 1B2 based on the correlation between the sample value closest to the zero cross at the NEG edge detected by the NEG zero cross detector 1B1 and each corresponding tap output. The sample value closest to the zero cross is set to a value that converges to zero.

The method of calculating the coefficient is disclosed in Japanese Unexamined Patent Publication No. 9-3216.
No. 71 can be referred to. Selection circuit 300
Is performed by the inclination determination circuit 400. That is, the inclination determination circuit 400 detects whether the read signal has a rising edge or a falling edge, generates a control signal corresponding to these, and sends either control signal to the selection circuit 300. They indicate whether a system should be selected.

Therefore, if the read signal exhibits a rising edge, the selection circuit 300 selects the first filter control system 1A, and the value of the coefficient kp from the POS edge coefficient control circuit 1A2 is set to the coefficient ki, and the FIR filter 100 On the other hand, if the read signal exhibits a falling edge, the selection circuit 300 selects the second filter control system 1B and outputs the coefficient kn from the NEG edge coefficient control circuit 1B2.
Is sent to the FIR filter 100 as the coefficient ki.

Thus, the FIR filter 100 can make a phase shift corresponding to the rising edge portion and the falling edge portion and corresponding to the appropriate threshold fluctuation amount and direction as described in FIG. An asymmetry-corrected read signal can be generated as an equalizer output. The inclination determination circuit 400 can have a specific configuration as shown in FIG.

In FIG. 10, the inclination determining circuit 400
Unit delay element 40 to which sample value series read signal is input
1, a subtractor 402 that subtracts the sample value of the delay output of the unit delay element 401 from the sample value of the input sample value sequence read signal, and a comparator 403 that compares the output value of the subtractor 402 with a reference value of zero. Be composed. The actual operation of the inclination determination circuit 400 can be represented by a time chart as shown in FIG.

That is, the subtractor 402 outputs a value obtained by subtracting the current read signal sample value from the previous read signal sample value, and the subtraction output obtained at the POS edge portion has a positive value. On the other hand, the subtraction output obtained at the NEG edge portion has a negative value. Therefore, the comparator 403 can recognize the positive or negative polarity by comparing the value of the subtraction output with zero, and recognizes the logical value 1 and the negative value when the positive value is recognized. In this case, a slope determination signal having a logical value of 0 is issued. Then, as shown in the figure, the filter coefficient is switched in accordance with the logical value indicated by the inclination determination signal.

When the inclination determining circuit is realized by an analog circuit, it can be configured as shown in FIG. The read signal is converted by the differentiating circuit 411 into a signal having a waveform corresponding to the gradient. The comparator 412 binarizes the waveform-converted signal using the zero level as a threshold, thereby obtaining a binary signal as shown in FIG. Can generate a gradient discrimination signal equivalent to that obtained by the above configuration.

FIG. 13 shows a configuration of a waveform equalizer according to the second embodiment, and the same reference numerals are given to the same parts as the configuration shown in FIG. In FIG. 8, the first and second
Input of the filter control systems 1A and 1B of the FIR filter 1
00, the input signal is supplied to the first and second filter control systems 1 and 2 as shown in FIG.
A configuration in which A and 1B are input can also be adopted.

With such a configuration, the same operation and effect as those of the waveform equalizer shown in FIG. 8 can be obtained. FIG. 14 shows a configuration of a waveform equalizer according to the third embodiment. Here, the same reference numerals are given to the same portions as those in the configuration shown in FIG. In FIG. 14, the inputs of the first and second filter control systems 1A and 1B are
0 for the POS edge and the NEG edge instead of the single FIR filter 100.
The FIR filters 101 and 102 are provided, the tap coefficients are individually controlled by the outputs of the corresponding filter control systems, and the selection circuit 300 selects one of the outputs of the FIR filters 101 and 102. ing.

With such a configuration, the same operation and effect as those of the waveform equalizer shown in FIG. 8 can be obtained. Although the digital waveform equalizer has been mainly described, the present invention is also applicable to an analog waveform equalizer. Although the 3T signal and the signal of 4T or more have been described in order to clearly show the problem of the present invention, the present invention is not limited to the signal of all run lengths regardless of the 3T signal and the signal of 4T or more. Is applied to

Further, the recording medium to which the present invention is applied is not necessarily limited to DVDs and CDs. In addition, various means have been described in a limited manner in each of the above-described embodiments, but can be appropriately modified within a range that can be designed by those skilled in the art.

[0042]

As described in detail above, according to the present invention,
A waveform equalizer capable of surely correcting asymmetry in a read signal and improving the quality of the read signal, and a data reproducing apparatus using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a time chart showing a mode of reading a recording signal without asymmetry.

FIG. 2 is a time chart showing a mode of reading a recording signal having asymmetry.

FIG. 3 is a graph showing a relationship between recording power on a disc and an eye pattern center position of a read signal.

FIG. 4 is a waveform diagram showing a difference between a 3T signal and a 4T or more signal when a recording signal with an under-recording power and an over-recording power is read.

FIG. 5 is a schematic block diagram of a data reproducing apparatus to which the waveform equalizer of one embodiment according to the present invention is applied.

FIG. 6 is a block diagram showing a basic configuration of a waveform equalizer according to one embodiment of the present invention.

7 is a waveform chart showing an asymmetry correction mode by the waveform equalizer of FIG. 6;

FIG. 8 is a block diagram showing a schematic configuration of a waveform equalizer according to a first embodiment configured according to the configuration of FIG. 6;

9 is a block diagram illustrating a configuration of an FIR filter in the waveform equalizer in FIG.

FIG. 10 is a block diagram illustrating a configuration example of a slope determination circuit in the waveform equalizer of FIG. 8;

FIG. 11 is a time chart for explaining the operation of the inclination determination circuit of FIG. 10;

FIG. 12 is a block diagram illustrating a modified example of the slope determination circuit in the waveform equalizer of FIG. 8;

FIG. 13 is a block diagram showing a schematic configuration of a waveform equalizer according to a second embodiment configured according to the configuration of FIG. 6;

FIG. 14 is a block diagram illustrating a schematic configuration of a waveform equalizer according to a third embodiment configured according to the configuration of FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 disc 2 spindle motor 3 optical pickup 4 RF amplifier 5 A / D converter 6 waveform equalizer 7 binarization circuit 10 POS equalizer 20 NEG equalizer 30 selection circuit 100 FIR filter 1A first filter control system 1A1 POS zero cross detection Circuit 1A2 Coefficient control circuit for POS edge 1B Second filter control system 1B1 NEG zero cross detection circuit 1B2 Coefficient control circuit for NEG edge 400 Slope discrimination circuit 300 Selection circuit D1 to D4 Unit delay element group M0, M1, M3, M4 Coefficient multiplication Unit A Adder 401 Unit delay element 402 Subtractor 403 Comparator 411 Differentiating circuit 412 Comparator 101 POS edge FIR filter 102 NEG edge FIR filter

Claims (5)

[Claims] 1. A waveform equalizer for performing waveform equalization on a read signal, comprising: slope determining means for determining a rising slope portion and a falling slope portion of the read signal; and a filter for performing a filtering process on the read signal. And a characteristic switching means for switching a frequency characteristic of the filter in accordance with a discrimination output of the inclination discriminating means. 2. The filter according to claim 1, further comprising: a first filter for setting a frequency characteristic for the rising slope, and a second filter for setting a frequency characteristic for the falling slope.
2. The waveform equalizer according to claim 1, wherein said characteristic switching means selects an output signal of one of said first and second filters and uses it as an output signal of a waveform equalizer. 3. The waveform or the like according to claim 1, wherein said filter is an FIR filter, and said characteristic switching means switches said frequency characteristic by changing a value of a tap coefficient of said FIR filter. Chemist. 4. The frequency characteristic under the discrimination of the rising slope is set according to a sample value near zero crossing in the corresponding rising slope of the read signal, and the frequency characteristic under the discrimination of the falling slope is determined. 4. The waveform equalizer according to claim 1, wherein said signal is set in accordance with a sample value near a zero cross at a corresponding falling slope of said read signal. 5. A data reproducing apparatus for binarizing a read signal from a recording medium to obtain reproduced data, wherein the sampling means samples the read signal to generate a sample value sequence read signal, and the sample value sequence read. A slope discriminating means for discriminating a rising slope portion and a falling slope portion of a signal, a filter for performing a filtering process on the sample value sequence read signal, and a characteristic switch for switching a frequency characteristic of the filter in accordance with a discrimination output of the slope discriminating means. And a binarizing means for binarizing an output signal of the waveform equalizer to generate the reproduced data.